It is known in the art that electrically conductive brushes have a number of uses. For example, a U.S. Pat. No. 3,691,993, to Krause et al, metallized fiber brush roller, made of metal fibers or nonmetallic fibers which are provided with a conductive coating, is subjected to a D.C. bias voltage for use in the image transfer operation in an electrostatic copying machine. Similarly, in copending application of Hugh Murray and Lawrence M. Marks, for "Charge Process with a Carbon Fiber Brush Electrode", Ser. No. 174,783, filed Aug. 4, 1980, assigned to the assignee of the present application and the disclosure of which is hereby incorporated by reference, there is disclosed a contact charging method using a carbon fiber brush electrode. Other uses for conductive brushes are also known. Accordingly, there is a need for an improved, economical and efficient method for making conductive brushes, and a need for the conductive brushes so produced.
In Hules U.S. Pat. No. 3,689,117, there is disclosed a method for making a brush for neutralizing static electrical charges from electrically conductive carbonaceous filaments, which involves the winding of carbon filaments around two rods mounted on two rotating end plates. After the winding is completed, a potting compound is applied to the outside of the windings over the rods. A U-shaped shield is then placed over each of the rods and the carbon filaments between the two rods is cut in half to form two brushes. The present invention provides an improved method for producing the conductive brushes. For example, in the method of Hules, the carbon filaments are caused to make two U-turns for each revolution of the winding apparatus. Since the rods on which the filaments are wound are of small diameters, the carbon filaments tend to break and thus to interrupt the winding process. Again, the method of Hules is adopted for making two brushes at one time, and it would be desirable to make a larger number of brushes for each winding operation. Another difficulty with the Hules method resides in the fact that brushes made by that method tend to have the strands of filaments not entirely perpendicular with respect to the conductive shield, but tend to be slightly slanted.
As indicated above, in Krause et al U.S. Pat. No. 3,691,993, there is disclosed the use of a D.C. biased metallized fiber brush roller for image transfer in an electrostatic copying machine. The metallized fibers of Krause et al are metal fibers, such as stainless steel fibers, and synthetic fibers, such as dynel and rayon fibers coated with a conductive material.
In Jeromin U.S. Pat. No. 3,877,417, there is disclosed brushes mounted on transfer corotron housing in an electrostatic copying process, to apply even pressure on the transfer medium to urge it against the surface of the photoconductive member. The brushes of Jeromin may be made of conductive or nonconducting materials.
In Kline U.S. Pat. Nos. 3,900,591 and 3,993,021, there is disclosed an image transfer device, which has a top layer of an electrically conductive fuzz fabric. The preferred fabric is a metal impregnated natural or synthetic fiber pile fabric, such as a silver impregnated polyamide pile fabric.
In Kohler U.S. Pat. No. 4,031,188, there is disclosed a process for forming carbonaceous fibers from polyacrylonitrile fibers, in which the polycarylonitrile is treated with an amine, oxidized at an elevated temperature, and carbonized by heating it to a temperature at least 1000.degree. C.
Finally, Japanese patent application Nos. 53-102630 and 53-102631, both in the name of Yoshisuke Takekida and assigned to Nippon Denki K.K. and filed Aug. 22, 1978, which were published under Nos. 55-29837(A) and 55-29838(A) on March 3, 1980, disclose a charging and transfer device for electrophotography which is made of a bundle of conductive thin fibrous wires shaped into a brush form by means of a holder in the shape of an open channel. Copies of the translated abstracts of these Japanese applications, in the form available to the present applicants, are attached to this application.
While the prior art methods for making conductive brushes, particularly the method of Hules, have been effective in making certain conductive brushes, there is a continuing need for improved and economical methods for making such conductive brushes.
Accordingly, it is an object of the present invention to provide an improved and efficient method for making conductive brushes.
It is another object of the present invention to provide an economical method for making conductive brushes of carbon fibers.
These and other objects of the invention can be gathered from the following detailed disclosure.